Solid-state imaging device and method for manufacturing the same

ABSTRACT

Channel stop sections are formed by multiple times of impurity ion implanting processes. Four-layer impurity regions are formed across the depth of a semiconductor substrate (across the depth of the bulk), so that a P-type impurity region is formed deep in the semiconductor substrate; thus, incorrect movement of electric charges is prevented. Other four-layer impurity regions of another channel stop section are decreased in width step by step across the depth of the substrate, so that the reduction of a charge storage region of a light receiving section due to the dispersion of P-type impurity in the channel stop section is prevented in the depth of the substrate.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application(s)No(s). P2002-330150 filed Nov. 14, 2002, which application(s) is/areincorporated herein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging device formed byintegrating a plurality of photosensors on a substrate in which achannel stop section for preventing leakage of electric charges betweenthe photosensors can be effectively formed and to a method formanufacturing the same.

2. Description of the Related Art

FIG. 6 is an explanatory view of an example of the arrangement of a CCDsolid-state imaging device.

The solid-state imaging device includes a photosensor (imaging region)410, a CCD vertical transfer section 420, a CCD horizontal transfersection 430, an output 440 and so on in a substrate 400.

The photosensor 410 has a plurality of the CCD vertical transfersections 420 along the respective photosensor trains, in which signalcharges stored by the photosensors 412 are output to the CCD verticaltransfer sections 420 and sequentially transferred in the verticaldirection by the driving of the CCD vertical transfer sections 420.

The CCD vertical transfer sections 420 have the CCD horizontal transfersection 430 at the end, in which the signal charges transferred from theCCD vertical transfer sections 420 are output to the CCD horizontaltransfer sections 430 line by line and sequentially transferred in thehorizontal direction by the driving of the CCD horizontal transfersections 430.

The output 440 receives the signal charges transferred by the CCDhorizontal transfer sections 430 by a floating diffusion (FD), sensesthe potential of the FD by an amp transistor, and converts it to anelectric signal for output.

The solid-state imaging device has a channel stop section for preventingcharge leakage between the pixels along the vertical transfer direction(along the column of the photosensors) and the photosensor and betweenthe photosensors along the horizontal transfer direction (along the rowof the photosensors) and the CCD vertical transfer section (for example,refer to Japanese Unexamined Patent Application Publication No.4-280675).

FIG. 7 is a sectional view of an embodiment of the channel stop sectionprovided between the photosensors along the vertical transfer direction,showing a section taken along line A—A of FIG. 6.

As shown in the drawing, a photodiode region constituting a photoreceiving section 510 of each photosensor has a P+ type impurity region510A formed in the outer layer of a substrate 400 and an N-type impurityregion 510B formed under the P+ type impurity region 510A.

Channel stop sections 520, or P-type impurity regions, are provided inthe vicinity of opposite sides of the photodiode region along thevertical transfer direction.

Although transfer electrodes 550 of the CCD vertical transfer sections420 and so on are provided on the top of the substrate 400 through agate insulating film (not shown), their detailed description will beomitted here because they are not directly related to the presentinvention.

FIG. 8 is a sectional view of an embodiment of the channel stop sectionprovided between a photosensor along the horizontal transfer directionand the vertical transfer section, showing a section taken along lineB—B of FIG. 6.

As shown in the drawing, the photodiode region of each photosensorincludes the P+ type impurity region 510A and the N-type impurity region510B, as that shown in FIG. 7.

The CCD vertical transfer section 420 is formed on the side of thephotodiode region through a readout gate.

The CCD vertical transfer section 420 is formed of an upper N-typeimpurity region 420A and a lower P-type impurity region 420B.

A channel stop section 520 that is a P-type impurity region is providedbetween the CCD vertical transfer section 420 and the photodiode regionof the adjacent photosensor train.

The above-described solid-state imaging device has a conspicuoustendency to reduce the space between the vertical and horizontalphotosensors with the reduction of the photosensor size owing toincreasing number of photosensors and advancement towardminiaturization.

Therefore, the structure of the related-art channel stop section that isformed only in the outer layer of the substrate has the problem of noteffectively preventing a phenomenon in which electric charges that arephotoelectrically converted in the photodiode region are mixed to theadjacent photosensors (hereinafter, referred to as a color mixingphenomenon).

In order to prevent the color mixing phenomenon, it is necessary toincrease energy during implantation of impurity ions to the channel stopsection to thereby form the channel stop section deep in the substrate(along the depth of the bulk). However, when ions are implanted withhigh energy, the P-type impurity near the surface declines inconcentration and so a smear component in the surface of the substratecannot be reduced, leading an adverse smear phenomenon.

The ion plantation with high energy has the problem of easily causingdispersion of the P-type impurity, narrowing a charge storage region ofthe light receiving section (photodiode region), which decreasessensitivity and saturation signals.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod for manufacturing a solid-state imaging device that provides ahigh quality image by forming a channel stop section that is effectivein miniaturization of photosensors to prevent a color mixing phenomenonand so on.

By a method for manufacturing a solid-state imaging device, according tothe present invention, a channel stop section is formed by multipletimes of ion implantation with multiple implanting energies. Thus, amultilayer impurity region can be formed across the depth of a substrateto form a channel stop section.

Therefore, the leakage of signal charges between adjacent photosensorsand between a photosensor and a transfer section can be effectivelyprevented; thus, a color mixing phenomenon can be effectively prevented.

Since multiple times of ion implantation are made for multipleimplantation areas during multiple times of impurity ion implantingprocesses, the dispersion of impurity particularly deep in the substratecan be prevented, effects to a photoelectric conversion section can bereduced, and decreases in sensitivity and saturation signals can beeffectively prevented.

Since the multiple times of ion implantation are made at multiple ionconcentrations during multiple times of impurity ion implantingprocesses, the impurity regions of the respective layers of the channelstop section can be given optimum impurity concentration; thus,anti-smear measures on the surface of the substrate can be effectivelytaken.

Since a solid-state imaging device according to the invention includes achannel stop section having multiple layers across the depth of thesubstrate, the leakage of signal charges between adjacent photosensorsand between a photosensor and a transfer section can be effectivelyprevented; thus, a color mixing phenomenon can be effectively prevented.

Since the areas of the multiple layers of the channel stop section aremultiple, the dispersion of impurity particularly deep in the substratecan be prevented, effects to a photoelectric conversion section can bereduced, and decreases in sensitivity and saturation signals can beeffectively prevented.

Furthermore, since the ion concentrations of the multiple layers of thechannel stop section are optimum, anti-smear measures on the surface ofthe substrate can be effectively taken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a solid-state imaging device along thevertical direction according to an embodiment of the present invention;

FIG. 2 is a sectional view of the solid-state imaging device along thehorizontal direction according to the embodiment of the presentinvention;

FIG. 3 is a sectional view of a solid-state imaging device along thevertical direction according to another embodiment of the presentinvention;

FIG. 4 is a sectional view of a solid-state imaging device along thevertical direction according to yet another embodiment of the presentinvention;

FIG. 5 is a sectional view of a solid-state imaging device along thevertical direction according to still another embodiment of the presentinvention;

FIG. 6 is a plan view of the arrangement of a CCD solid-state imagingdevice;

FIG. 7 is a sectional view of a related-art solid-state imaging devicealong the vertical direction; and

FIG. 8 is a sectional view of the related-art solid-state imaging devicealong the horizontal direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a solid-state imaging device and a method formanufacturing the same according to the present invention will bespecifically described hereinafter.

FIGS. 1 and 2 are sectional views of a solid-state imaging devicemanufactured by the method according to an embodiment, FIG. 1 showing anembodiment of a channel stop section provided between photosensors alongthe vertical transfer direction, and FIG. 2 showing an embodiment of achannel stop section provided between the photosensors along thehorizontal transfer direction. The entire structure of the solid-stateimaging device is the same as that of the related art shown in FIG. 6,wherein FIG. 1 corresponds to the section taken along line A—A of FIG. 6and FIG. 2 corresponds to the section taken along line B—B of FIG. 6.

Referring first to FIG. 1, a photodiode region constituting a lightreceiving section 10 of each photosensor includes a P+ type impurityregion (hole storage region) 10A formed in the outer layer of asubstrate 100 and an N-type impurity region (electron storage region)10B formed under the P+-type impurity region 10A. The photodiode regionphotoelectrically converts light that is incident from above, absorbsholes into the P+ type impurity region 10A, and stores electrons in theN-type impurity region 10B, a lower depletion layer and so on.

The photoelectric conversion in the light receiving section 10 is mainlyperformed in a depletion region between the N-type impurity region 10Band the P+ type impurity region 10A and in a depletion region betweenthe N-type impurity region 10B and a lower P-type impurity region (notshown).

A channel stop section 20 formed of a multilayer P-type impurity regionis provided in the vicinity of opposite sides of the photodiode regionalong the vertical transfer direction.

The channel stop section 20 is formed by multiple times of impurityimplanting processes by which four impurity regions 20A, 20B, 20C, and20D are formed across the depth of the substrate 100 (along the depth ofthe bulk) to form a P-type region deep in the substrate 100, therebypreventing leakage of electric charges.

Referring to FIG. 2, the photodiode region of each photosensor includesthe P+ type impurity region 10A and the N-type impurity region 10B, asthat shown in FIG. 1.

A CCD vertical transfer section 40 is formed on the side of thephotodiode region through a readout gate.

The CCD vertical transfer section 40 is formed of an upper N-typeimpurity region 40A and a lower P-type impurity region 40B.

A channel stop section 50 that is a multilayer P-type impurity region isprovided between the CCD vertical transfer section 40 and the photodioderegion of the adjacent photosensor train.

The channel stop section 50 is formed by multiple times of impurityimplanting processes by which four impurity regions 50A, 50B, 50C, and50D are formed across the depth of the substrate 100 (along the depth ofthe bulk) to form a P-type region deep in the substrate 100, therebypreventing leakage of electric charges.

In FIGS. 1 and 2, transfer electrodes 60 of the CCD vertical transfersections 40 and so on are provided on the top of the substrate 100through a gate insulating film (not shown). However, their detaileddescription will be omitted here because they are not directly relatedto the present invention.

When the channel stop sections 20 and 50 are formed in theabove-described solid-state imaging device, an ion implantation regionis set using a specified mask and multiple times of ion implantingprocesses are performed with multiple ion implanting energies andimpurity concentrations, so that the multilayer impurity regions 20A,20B, 20C, and 20D and the impurity regions 50A, 50B, 50C, and 50D areformed.

Thus, the channel stop sections 20 and 50 can be formed deep into thesubstrate 100, thereby preventing the leakage of signal charges betweenthe devices to reduce color mixture.

Since the concentration of impurity in each ion implanting process canbe set as appropriate, the concentration of impurity near the surface ofthe substrate 100 that is formed with low implanting energy can besufficiently ensured by making the ion concentration of impurity in anion implanting process with relatively high implanting energy higherthan that in an ion implanting process with relatively low implantingenergy, so that a smear phenomenon can be prevented.

When the solid-state imaging device is formed, ions are continuouslyimplanted into the substrate 100 to form the photodiode region (lightreceiving section 10), the CCD vertical transfer section 40, and therespective impurity regions of the channel stop sections 20 and 50; theorder thereof is not particularly limited.

Also the order of the multiple times of ion implanting processes forforming the channel stop sections 20 and 50 is not particularly limited.

The mask for ion implantation includes various types in addition to ageneral resist mask; therefore, it is not particularly limited.

A specific energy and the concentration of impurity in each ionimplanting process can be set as appropriate and are not particularlylimited.

In the embodiment, the vertical channel stop section 20 and thehorizontal channel stop section 50 are separately formed so as to beoptimized for the respective required characteristics, with individualion implanting energy and impurity concentration. In FIGS. 1 and 2,although both the channel stop sections 20 and 50 have four-layerstructure (or four-step ion implantation), they are not limited to thatand may have a structure other than the four-layer (four-step)structure. The vertical channel stop section 20 and the horizontalchannel stop section 50 may not necessarily have the same number oflayers.

The impurity concentration may not be varied at all the layers but maybe varied at part of the layers.

In the above embodiment, the ion implanting processes for forming thechannel stop sections 20 and 50 are carried out with multiple energiesand concentrations. However, the ion implantation region is varied ineach ion implanting process by changing a mask in each ion implantingprocess, so that the width across the channel of the respective impurityregions of the channel stop sections 20 and 50 may be varied.

FIG. 3 is a sectional view of an example of the channel stop sectionalong the vertical transfer direction. Since components other than achannel stop section 70 are the same as those of FIG. 1, they are giventhe same numerals and there description will be omitted.

As shown in the drawing, the channel stop section 70 includes four-layerimpurity regions 70A, 70B, 70C, and 70D. When the ion implanting area inan ion implanting process with relatively high implanting energy is madesmaller than that in an ion implanting process with relatively lowimplanting energy, the reduction of the charge storage region of thelight receiving section 10 in the deep part of the substrate 100 by thedispersion of P-type impurity of the channel stop section 70 can beprevented; thus, sensitivity of the light receiving section 10 andsaturation signals can be increased.

The energy and the impurity concentration can be set as those in FIG. 1.

Although the widths of all the layers of the channel stop section 70 maybe varied, only the width of part of the layers may be varied so thatonly the impurity regions 70A and 70B have the equal width, as shown inFIG. 3. In this case, the layers of an equal width can be formed with acommon mask.

The multi-step ion implantation may also be made for the channel stopsection along the horizontal transfer direction, with multiple widths.

The above-described embodiments offer the following advantages:

(1) Referring to FIGS. 1 to 3, when multi-step ion implantation of thechannel stop section between the vertical photosensors and the channelstop section between the horizontal light receiving section and thevertical transfer section is carried out with multiple energies, a colormixing phenomenon can be prevented in which photoelectrically convertedcharges are mixed to the adjacent photosensors.

(2) Referring to FIG. 3, when the region of ion implantation with highenergy reduced, a color mixing phenomenon can be prevented withoutnarrowing the charge storage region of the light receiving section anddecreasing sensitivity and saturation signal.

(3) Referring to FIGS. 1 to 3, when ions are implanted into the channelstop section with high energy, the variation of an overflow barrier atcharge storage can be reduced; thus the occurrence of a knee-point(Qknee) in output characteristics can be prevented.

(4) When ion implantation of the channel stop section between thehorizontal light receiving section and the vertical transfer section iscarried out with multiple energies, a smear phenomenon near the surfaceand in the bulk can be prevented.

In the above-described embodiments, the positional relationship of themulti-step ion implanted impurity regions is only an example, and thethickness of the impurity regions across the depth of the substrate, theshape, and the number of layers are not limited to that. For example, asshown in FIG. 4, of the multilayer impurity region of a channel stopsection 80 (three-layer impurity regions 80A, 80B, and 80C in thedrawing), the middle-layer impurity region (the impurity region 80B inthe drawing) may be larger in thickness and also in lateral width thanthe other impurity regions or vice versa.

As a matter of course, the multilayer ion-implanted impurity region mayhave a part overlapping with the upper and lower impurity regions in thestrict sense.

In the above embodiments, although the multilayer ion-implanted impurityregion is formed such that the bottom of the lowermost-layer region hasa depth substantially equal to that of the bottom of the N-type impurityregion 10B in the light receiving section 10, it is not limited to that.

For example, in order to prevent color mixture in a further lower regionacross the depth of the substrate 100, as shown in FIG. 5, the bottom ofthe lowermost-layer region (an impurity region 90D in the drawing) ofthe multilayer ion-implanted impurity region (four-layer impurityregions 90A, 90B, 90C, and 90D in the drawing) of a channel stop section90 may be formed deeper than the bottom of the N-type impurity region10B.

As shown in FIG. 5, an overflow barrier 92 located below the lightreceiving section 10 and the multilayer ion-implanted impurity region(the impurity region 90D in the drawing) may be in contact with eachother.

In this case, the holes stored in the overflow barrier 92 can bedischarged to the surface of the substrate 100 through the multilayerion-implanted impurity region. The multilayer ion-implanted impurityregion is preferably formed such that the closer to the surface of thesubstrate 100 the region is, the higher the concentration of the P-typeimpurity is.

Although a preferred form of the invention has been described in whichit is applied to a CCD solid-state imaging device, it is to beunderstood that the invention is applied not only to the CCD solid-stateimaging device but also to a CMOS solid-state imaging device.

As described above, by the method for manufacturing the solid-stateimaging device according to the invention, the channel stop section isformed by multiple times of impurity ion implanting processes withmultiple implanting energies. Thus, a multilayer impurity region can beformed across the depth of the substrate as a channel stop section.

Therefore, leakage of signal charges between the adjacent photosensorsand between the photosensor and the transfer section can be effectivelyprevented, so that a color mixing phenomenon and so on can beeffectively prevented.

During the multiple times of impurity ion-implantation processes, theion implantation is carried out for multiple implantation areas, so thatthe dispersion of the impurity can be reduced particularly deep in thesubstrate, the effects to the photoelectric conversion section can bereduced, and decreases in sensitivity and saturation signals can beeffectively prevented.

Furthermore, during the multiple times of impurity ion-implantationprocesses, the ion implantation is carried out at multiple impurityconcentrations, so that the respective impurity regions of the channelstop section can be formed at optimum impurity concentrations; thusanti-smear measures on the surface of the substrate can be effectivelytaken.

Since the solid-state imaging device according to the invention includesa channel stop section having a multilayer impurity region across thedepth of the substrate, leakage of signal charges between the adjacentphotosensors and between the photosensor and the transfer section can beeffectively prevented; thus, a color mixing phenomenon and so on can beeffectively prevented.

Since the multilayer impurity region of the channel stop section hasmultiple areas, the dispersion of impurity particularly deep in thesubstrate can be prevented, the effects to the photoelectric conversionsection can be reduced, and decreases in sensitivity and saturationsignals can be effectively prevented.

Furthermore, the multilayer impurity region of the channel stop sectionhas an optimum impurity concentration at each layer; thus anti-smearmeasures on the surface of the substrate can be effectively taken.

1. A method for manufacturing a solid-state imaging device comprisingthe steps of: forming a photosensor in the surface of a substrate; andforming a channel stop section comprising a plurality of impurityregions adjoining each other on the side of the photosensor in thesubstrate by multiple times of ion implantation with multiple implantingenergies.
 2. A method for manufacturing a solid-state imaging deviceaccording to claim 1, wherein the multiple times of ion implantation aremade in multiple implantation areas.
 3. A method for manufacturing asolid-state imaging device according to claim 1, wherein the multipletimes of ion implantation are made in an equal implantation area.
 4. Amethod for manufacturing a solid-state imaging device according to claim1, wherein the multiple times of ion implantation are made at multipleion concentrations.
 5. A method for manufacturing a solid-state imagingdevice according to claim 1, wherein the multiple times of ionimplantation are made at an equal ion concentration.